The present disclosure relates to a tomographic image generation device, a tomographic image generation method and a tomographic image generation program for obtaining a plurality of projection images of a subject by imaging the subject with different radiation source positions, and generating a tomographic image from the projection images.
In recent years, in order to more closely observe an affected part of the body with a radiographic imaging apparatus using radiation, such as x-ray or γ-ray, tomosynthesis imaging has been proposed, in which imaging is performed by applying radiation to the subject from different radiation source positions by moving the radiation source, and the thus obtained projection images are added up to generate a tomographic image in which a desired slice plane is emphasized. In the tomosynthesis imaging, a plurality of projection images are obtained by imaging a subject with different radiation source positions by moving the radiation source in parallel with the radiation detector or along a circular or ellipsoidal arc trajectory depending on characteristics of the imaging apparatus and necessary tomographic images, and the projection images are reconstructed to generate a tomographic image using a simple reverse projection method, or a reverse projection method such as a filter reverse projection method.
When the above-described tomosynthesis imaging is performed, it is necessary to align the projection images obtained by the imaging with one another before reconstructing the projection images. For this purpose, techniques have been proposed which involve calculating the radiation source position with which each projection image is taken by equally dividing the range of movement of the radiation source by the number of shots, or by performing calibration by imaging an object with known three-dimensional coordinates, and reconstructing the projection images using information of the calculated radiation source positions.
With these techniques, however, it is difficult to accurately move the radiation source to the calculated radiation source positions, due to influence of a mechanical error, such as vibration during imaging or mechanical misalignment, and the radiation source positions during imaging may be different from the calculated radiation source positions. This positional error, or positional misalignment, hinders accurate alignment of the projection position of an object, resulting in degradation of the image quality of the tomographic image.
Further, with a radiation imaging apparatus that performs the above-described tomosynthesis imaging, a plurality of images of the subject are taken based on an instruction to start an imaging operation, and this imaging operation takes several seconds from the start to the of the imaging operation, during which the subject may move. When there is such a body motion of the subject, it is difficult to accurately align the projection position of the object during the reconstruction, resulting in degradation of the image quality of the tomographic image.
To address this problem, a technique has been proposed where the subject or the imaging table on which the subject is provided with a marker during the tomosynthesis imaging, and the marker is imaged together with the subject to obtain a plurality of projection images including the marker image (see Japanese Unexamined Patent Publication No. 2013-020023, hereinafter Patent Document 1). According to the technique taught in Patent Document 1, an accurate radiation source position and an accurate marker position are calculated for each projection image using positional information of the marker, and the projection images are reconstructed using the calculated radiation source position and marker position, to eliminate the influence of the positional error of the radiation source positions.
Further, a technique where a plurality of radiographic images which are sequentially obtained during the tomosynthesis imaging are displayed on a monitor to allow the operator to check whether or not there is a body motion, and a retake operation is performed if there is a body motion has been proposed (see Japanese Unexamined Patent Publication No. 2010-194297, hereinafter Patent Document 2).